Spring mattress



FIG. 1 is a perspective view of a spring mattress showing my new design;

FIG. 2 is a front view of the spring mattress shown in FIG. 1;

FIG. 3 is a rear view of the spring mattress shown in FIG. 1;

FIG. 4 is a left side view of the spring mattress shown in FIG. 1;

FIG. 5 is a right side view of the spring mattress shown in FIG. 1; and,

FIG. 6 is a top plan view of the spring mattress shown in FIG. 1.

The bottom view is omitted as forming no part of the claimed design.

Broken lines indicate unclaimed subject matter forming no part of theclaimed design.

CLAIM The ornamental design of a spring mattress, as shown anddescribed.